Synthesis And Characterization Of Iodates Nonlinear Optical Crystals With Mixed Anions

Nonlinear optical crystal materials which can effectively broaden the laser band has a wide application prospect in military and civilian,etc.The premise of nonlinear optical properties is that it has a non-centrosymmetric(NCS)structure.Iodates,which I⁵⁺cations with stereochemically active lone-pair(SCALP)electrons can result in the formation of NCS materials,have made the syntheses of new iodates being the current hotspots.At present,these researches mainly concentrated on complex cation iodates by introducing d~0 metal cation and metal cations containing SCALP to improve the structural distortion.The iodates with multiple anions,however,are still rarely reported.It has been noted that combining multi-type oxyanions in one structure is a valid strategy to improve the functional performance of materials.Therefore,in this paper,we mainly focus on the anions by introducing F^-anions with high electronegativity and[SO₄]^2-anion groups with rigid structure into the iodates to increase the structural distortion and improve the material band gap,respectively.And we obtained a series of novel compounds including Cs₂VOF₄(IO₂F₂)and Na₇(IO₃)(SO₄)₃.The researches are summarized as follows:1.Based on the heteroleptic polyhedral-mixing of[IO₂F₂]^-units,fluorinated iodate such as K₂VOF₄(IO₂F₂)and Cs₂VOF₄(IO₂F₂)were synthesizedF^-aions can partly substitute O^2-ligands in metal oxides to generate a larger structural distortion favoring for the large second harmonic generation(SHG)response of NLO crystals because that F^-anion has greater electronegativity than O^2-.We successfully synthesized two transition metal fluoroiodates K₂VOF₄(IO₂F₂)and Cs₂VOF₄(IO₂F₂)by hydrothermal method through understanding the law of fluorinated iodates,in which Cs₂VOF₄(IO₂F₂)exhibits an excellent NLO properties,is a potential nonlinear optical crystal material.The rules for synthesizing the different types of F-containing ETM iodates has been explained according to the valence matching principle.This discussion should give useful insight into the targeted syntheses of ETM fluoroiodates.2.Based on the homoleptic polyhedra-mixing between[IO₃]^-and[SO₄]^2-anionic units, the first non-centrosymmetric alkali-metal iodate-sulfate:Na₇(IO₃)(SO₄)₃ crystal was synthesizedThe combination between anionic groups can balance the properties of materials.In this paper,we introduced[SO₄]^2-tetrahedron into iodate system and successfully synthesized the first non-centrosymmetric alkali-metal iodate-sulfate Na₇(IO₃)(SO₄)₃.[SO₄]^2-group expanded the band gap of the compound to 4.83 e V,and[IO₃]^-group also increased the birefringence to 0.075@1064 nm.Therefore,combining and mixing multiple anions in one compound have been widely considered as one of the most effective strategies to synthesis the nonlinear optical crystal material.The synthesis of the compound further enriched the structural chemistry of compound anionic iodate.3.The synthesis of other iodate crystalsThree new iodate compounds Cs VO₂(IO₃)₂,Ba₂Zn(IO₃)₆ and Ba₂Mg(IO₃)₆were synthesized by hydrothermal method in the process of synthesizing hetero-anionic materials.Cs VO₂(IO₃)₂ has a moderate birefringence(0.066@1064nm)and had grown the millimeter-sized crystals in aqueous solution environment.Ba₂Zn(IO₃)₆ and Ba₂Mg(IO₃)₆have the similar structure with A₂Ti(IO₃)₆(A=Li,Na,K,Rb,CS),and can be regarded that the alkaline metal and Ti are substituted by alkaline-earth metal and Zn atom,respectively,improving moisture absorption characteristics and expanding the band gap.It can provide a new idea for the structural design of new iodate crystals based on the strategy of multi-element substitution.